Chronic rejection of transplanted organs remains the primary cause of graft failure over time despite advances in immunosuppression. Memory T cells and production of antibodies by B cells are recognized as important mediators of chronic rejection but are not effectively controlled by current immunosuppression regimens. We find that antibody-independent functions of B cells also play a significant role in the pathogenesis of alloimmunity and chronic rejection by presenting antigen and providing costimulation to T cells. Here, we will test the hypothesis that B cell interactions with T cells play a key role in the development, maintenance and recall of T cell memory. We propose to (a) delineate when, where and which B cells interact with T cells in shaping memory responses, and (b) test whether blocking these interactions will prevent chronic rejection. Non-selective targeting of B cells by global depletion strategies may be detrimental as it also removes B cells with regulatory functions. Understanding which specific B cell populations interact with T cells, when and where they function to sustain long-lived memory is therefore a clinically relevant and significant goal. Results from these proposed studies would allow us to develop novel therapies that inhibit T cell memory and prevent chronic rejection by targeting specific functions, subpopulations and/or migration of B cells.